Globally known phosphor receive energy from an excitation source having high energy, such as vacuum ultraviolet rays, ultraviolet rays, electron beams, near-ultraviolet rays, and blue rays, and emit visible rays in vacuum fluorescent displays (VFD), field emission displays (FED), plasma display panels (PDP), cathode ray tubes (CRT), and white light-emitting diodes (WLED). Among the above-mentioned applications, particularly, research on light-emitting diodes (LEDs), having advantages of high efficiency and environmental friendliness compared to conventional methods, has been actively carried out in accordance with the growing worldwide interest in environmental problems such as the recent global energy crisis and global warming.
In order to use an LED, which has clear advantages as a solid light source to replace a conventional light source, it is most important to realize high-quality white light, and accordingly, a phosphor having desirable properties is required. Methods for realizing white light using LEDs are broadly classified into three groups. The first method is to obtain a white LED by combining three LEDs respectively exhibiting red, green, and blue colors. In this method, since the emission wavelength spectrum is wide, color rendering is excellent. However, there are drawbacks that the operating voltage is uneven for each chip and the output of the chip depends on the ambient temperature, thus causing variability of color coordinates, and that the price is high. A second method is to obtain a white color by exciting a yellow fluorescent substance using a blue LED as a light source. In this method, since a simple structure including one chip and two terminals is used, manufacturing costs may be reduced and light emission efficiency is excellent. However, since the color rendering index is low due to poor emission of light in a red region, it is difficult to apply the second method to a high-quality solid light source. A third method is to obtain a white color by mixing blue, green, yellow, and red fluorescent substances using a near-UV LED as a light source. This method is very similar to the method of forming a fluorescent lamp using ultraviolet rays. In this method, a very wide wavelength spectrum is ensured, as in the case of an incandescent lamp, color stability is excellent, and it is easy to control the correlated color temperature and color rendering index. Accordingly, this method is currently being studied for the implementation of white LEDs for illumination.
The second method is the most popular method, but it is difficult to develop and utilize technology related to this method due to a patent held by Nichia Corporation in Japan. Therefore, there is a need to develop a high-efficiency phosphor to be combined with a near-UV LED. In particular, in the near-UV LED, a blue phosphor functions as an excitation source of a phosphor having a long wavelength (a green color to a red color), and thus the characteristics of the blue phosphor are important. Blue phosphor developed to date have good light emission efficiency but poor thermal stability at high temperatures during operation of the near-UV LED. Accordingly, it is difficult to apply such blue phosphor. Therefore, it is necessary to develop a blue phosphor having a novel composition, favorable light emission efficiency and thermal stability, without infringing on the patent of another phosphor.
Meanwhile, a Na3Sc2P3O12 crystal phase, which is one of NASICON structures, is a phosphate that is formed using a calcining process of NaHCO3—Sc2O3—(NH4)2HPO4 raw material for use as an ionic conductor. The formation of the Na3Sc2P3O12 crystal phase was confirmed by G. Collin et al. The formation process and mechanism of the Na3Sc2P3O12 crystal phase have been reported in detail in academic documents published prior to this application [1) M. de la Rochère et al., Solid State Ionics 9-10 (1983) 825-828. 2) G. Collin et al., Journal of Physics and Chemistry of Solids 47(9) (1986) 843-854]. The content of the report described in the above documents refers only to ionic conductivity, and no research has been performed so far on the use of this structure as a phosphor.